Method of producing aluminum composite material

ABSTRACT

A manufacturing method of an aluminum composite material having excellent abrasion resistant and vibration damping properties is disclosed. The aluminum composite material is manufactured by impregnating a perform with an aluminum alloy the perform is formed by mixing an alumina fiber and graphite or activated charcoal and an inorganic binder in water and sintering the resultant mixed product at a predetermined sintering temperature under vacuum, in an inert gas, or in a reducing gas.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a method of producing aluminum composite material produced by mixing an aluminum fiber and graphite or activated charcoal to an aluminum alloy.

(2) Description of the Background Art

An aluminum alloy has been optimally used in devices including such as automobiles, electric appliances, electronic parts, and precious measurement equipment because of its lightness and malleability. Nevertheless the application of the aluminum alloy is limited to a sliding portion of structure because of low resistance to abrasion. Further, especially in an automobile, comfortable ride and driving performance are not well achieved due to noise and vibration because an aluminum alloy has lower vibration damping property than a cast iron. Accordingly, various composite materials such as graphite and activated charcoal with superior lubricating property and damping property have been added to promote resistance to abrasion and vibration damping property.

A composition in which activated charcoal and ceramic such as alumina particle and alumina fiber are dispersed in aluminum alloy material was disclosed in Japanese Laid Open Patent Publication No. S58-81948. Further, a method of manufacturing the composite material was disclosed in Japanese Laid Open Patent Publication No. H6-24035 in which a compact which was obtained by dehydration or de-alcoholization after aluminum short fiber and graphite were mixed with water or alcohol, and an aluminum alloy was made into a complex.

In both method of an aluminum composite material by mixing activated charcoal or graphite to hot melting aluminum alloy solution disclosed in S58-81948 above and method of an aluminum composite material by impregnating hot melting aluminum alloy solution to an preform prepared by sintering an alumina fiber with activated charcoal or graphite disclosed in H6-24035 above, the activated charcoal or the graphite are exposed to high temperature because of using such hot solution or sintering of aluminum alloy. In the air activated charcoal and graphite can be characteristically easily oxidized and the oxidation of activated charcoal and graphite vigorously proceeds over approximately 600° C., and are lost as carbon dioxide or carbon monoxide. Even though heating over 600° C. by hot solution or sintering of aluminum alloy are used in the methods above, no means to prevent the oxidation of activated charcoal or graphite was disclosed and accordingly the oxidation-loss of activated charcoal and graphite could not be prevented. Thus it was difficult to obtain an aluminum alloy composite material having excellent abrasion resistant and vibration damping properties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a)-1(c) are figures illustrating a preform forming process of the invention.

FIGS. 2(a)-2(d) are figures illustrating an aluminum impregnating process of the invention.

FIG. 3 is a figure showing the evaluation results of an abrasion resistant property, a vibration damping property and hardness of aluminum composite material 4 according to each embodiment and comparison embodiment of the invention.

FIG. 4 is a figure illustrating a structural photograph of aluminum composite layer 12 a according to embodiment 1 of the invention.

FIG. 5 is a figure illustrating a structural photograph of aluminum composite layer 12 a according to comparison embodiment 1 of the invention.

DETAIL DESCRIPTION OF THE INVENTION

According to the invention, a method of manufacturing an aluminum composite material which has excellent abrasion resistant and vibration damping properties is disclosed.

According to an implementation of the invention, the method of manufacturing the aluminum composite material comprises steps of mixing an alumina fiber, graphite and an inorganic binder in water; dehydrating and forming; preform forming process which forms the preform by sintering the mixture at a designated temperature under vacuum, in an inert gas or in a reducing gas; and then an aluminum impregnating process which impregnates the perform with an aluminum alloy by pressure casting.

Further, according to an implementation of the invention, the method of manufacturing the aluminum composite material comprises steps of mixing an alumina fiber, activated charcoal and an inorganic binder in water; dehydrating and forming; preform forming which forms a preform by sintering the mixture at a designated temperature under vacuum, in an inert gas or in a reducing gas; and then an aluminum impregnating process which impregnates the perform with an aluminum alloy by pressure casting.

According to two manufacturing methods, a formed base material obtained by dehydrating and forming the aqueous mixture solution of the alumina fiber, graphite or activated charcoal, and the inorganic binder has almost an homogeneous structure of the alumina fiber and graphite or activated charcoal because graphite and activated charcoal can be coagulated to the alumina fiber by addition of the inorganic binder. Further an oxidation-loss of graphite or activated charcoal over approximately 600° C. can be prevented by heating and sintering the dehydrated-formed base material at the designated sintering temperature under vacuum, in an inert gas or in a reduced gas, and accordingly a preform appropriately having graphite or activated charcoal can be formed. Further a heat-contraction of the preform can be prevented because graphite or activated charcoal does not either coagulate or react with the alumina fiber when it is heated under vacuum, in an inert gas or in a reducing gas. Accordingly a preform having high strength and high breathability can be formed because the temperature of sintering the alumina fiber can be raised farther. Accordingly the preform formed by processing to form the preform above comprises structure dispersing graphite and activated charcoal almost in homogeneous with an excellent strength and breathability.

The hot solution of aluminum alloy is pressurized and cast to the preform above having high strength and high breathability by an impregnation process. Crush of the preform can be prevented because the preform formed in the preform forming process has high strength and the aluminum alloy, the aluminum fiber and graphite or activated charcoal can make a complex almost in homogeneous. The hot solution of aluminum is easily impregnated because the preform has high breathability and occurrence of voids of the composite material after forming can be adequately prevented. Specifically according to the preform forming process and aluminum impregnation process, the aluminum composite material having excellent abrasion resistant and vibration damping properties can be obtained with graphite or activated charcoal which are existing almost in homogenous and dispersedly.

Further the aluminum composite material manufactured according to the method of the invention has a low thermal expansion coefficient because graphite or activated charcoal has a low thermal expansion coefficient and also the thermal expansion coefficient of alumina fiber is low, and accordingly a thermal deformation occurs unlikely and excellent form stability can be achieved. Further the aluminum composite material manufactured by mixing graphite can retain the excellent thermal conductivity coefficient of aluminum alloy because graphite has relatively a high thermal conductivity coefficient.

Further such as alumina sol, silica gel and lithium silicate as an inorganic binder can be applied adequately. When such inorganic binder is used, the mixed alumina fiber and graphite or activated charcoal powder in water can coagulate with sufficient strength by hydration. Further the aluminum composite material is that alumina fiber, graphite or activated charcoal are combined with sufficient adhesion because of excellent adhesion of such inorganic binder, and accordingly father excellent abrasion resistant and vibration damping properties can be obtained.

According to another implementation of the invention disclosed in claim 3, the manufacturing method is using graphite above having particle diameters in the range of 0.1 μm to 100 μm. Also another implementation of the invention disclosed in claim 4, the manufacturing method is using activated charcoal above having particle diameters in the range of 0.1 μm to 100 μm. The preform in which graphite or activated charcoal are dispersedly fixed almost in homogeneous to aluminum fiber by using designated amount of graphite or activated charcoal having such particle diameters can be obtained, and also area of adhesion for graphite or activated charcoal and aluminum alloy can be secured and accordingly the aluminum composite material which can carry out farther adequately an abrasion resistant property and a vibration damping property can be obtained. If a particle diameter of graphite or activated charcoal is larger than 100 μm, it is difficult that graphite or activated charcoal are dispersed homogeneously and an distance between each graphite or activated charcoal in the aluminum composite material becomes longer and each graphite or activated charcoal would be separated, and accordingly it is difficult that the abrasion resistant property and the vibration damping property are carried out sufficiently. Further if the particle diameter is large, graphite or activated charcoal would not be sintered. Therefore parts having relatively weak strength occupy large area and volume of preform becomes large, and accordingly strength of the preform becomes insufficient. Therefore it may take place that preform is easily crushed during the pressurized casting process in aluminum impregnation process and an adequate aluminum composite material could not be formed. Graphite or activated charcoal having particle diameter larger than 0.1 μm which is relatively easily obtainable is used. If the particle diameter is smaller than 0.1 μm, graphite or activated charcoal easily floats and cannot be equally mixed by stirring because graphite or activated charcoal is given larger surface tension from water in comparison with its weight during being mixed with aluminum fiber in water. Further, it is preferable that the particle diameter is larger than 5 μm in order to secure sufficient area for adhesion and to perform an adequate binding property. Further, it is more preferable that graphite or activated charcoal having particle diameter in the range of 5 μm to 50 μm is used in order to form farther adequate aluminum composite material. Even though particle diameters of some graphite or activated charcoal are more or less over than the range, it can be included in the invention because a targeted aluminum composite material can be obtained.

According to another implementation of the invention, the manufacturing method is for activated charcoal above having a porous structure; wherein a binding strength of aluminum alloy and activated charcoal is farther strengthened because the aluminum alloy can be impregnated into pores of activated charcoal in aluminum impregnation process.

According to another implementation of the invention, the manufacturing method is for the alumina fiber having an average diameter in the range of 1 μm to 10 μm and the average length of 10 cc/5 gf to 100 cc/5 gf. The average length of alumina fiber is defined as a volume per weight unit because the alumina fiber is generally complex and intertwined. The preform can be formed with adequate compact density by using such average diameter and average length, and accordingly the preform can be excellently strong and breathable. If an average diameter of the alumina fiber is larger than 10 μm, the preform is easily crushed because the volume is large and the strength of the preform is insufficient. If an average length of the alumina fiber is larger than 100 cc/5 gf, a deformation and breaking easily take place because the compact density of the preform is lower and the strength of the preform is insufficient. Further, if the average diameter is smaller than approximately 1 μm or the average length is smaller than approximately 10 cc/5 gf, an defect can easily take place because breathability of the perform is insufficient and the preform cannot sufficiently impregnate the aluminum alloy. Preferably the average diameter is in the range of 1 μm to 5 μm and the average length is in the range of 20 cc/5 gf to 60 cc/5 gf in order to form the preform which has farther excellent strength and breathability. Further, even if some alumina fiber out of the range more or less is mixed, the targeted aluminum composite material can be obtained and accordingly these are also covered by the invention.

According to another implementation of the invention, a sintering temperature of the manufacturing method in the preform forming process is in the range of 600° C. to 1600° C. According to such temperature, an preform having high strength can be formed and also the preform can be bound with sufficient force to the aluminum alloy which is impregnated in the following impregnation process because crystal water of the alumina sol and silica gel used as an inorganic binder can be evaporated and the adhesion property of the alumina fiber and graphite or activated charcoal can be increased. If the temperature is below 600° C., strength of the preform can be insufficient because the evaporation of crystal water of the inorganic binder is insufficient and the alumina fiber cannot be sintered sufficiently. Further, if the temperature is higher than 1600° C., the time to reach to a constant temperature and the time to cool down takes too long to be industrially and practically acceptable from such as productivity standpoint of view. More preferably the temperature in the range of 900° C. to 1200° C. is used in order to form the preform having high strength and increase the adhesion of the alumina fiber and graphite or activated charcoal in a good balance.

According to an implementation of the invention, a manufacturing method that the impregnating process above forms a layering structural material of a complex material layer impregnating the aluminum alloy to the preform and the aluminum alloy layer is disclosed. In such manufacturing method, the layering structural material comprising a complex material obtained by which the aluminum alloy impregnates to the preform and an aluminum alloy layer solidified without impregnating to the prefonr is formed by using a hot solution of the aluminum alloy used in pressurized casting which is more than an impregnating volume to the preform. Accordingly, the layering structural material comprising the aluminum composite material above having excellent abrasion resistant and vibration damping properties and the aluminum alloy can be easily formed and the layering structural material has a structure in which strength between layers is excellent because the composite material layer and the aluminum alloy layer are integrally formed.

EMBODIMENTS

The inventor describes embodiments of the invention referring to figures.

Referring to FIG. 1, a preform forming process which forms the preform of the invention is illustrated and referring to FIG. 2, an aluminum impregnating process which impregnates preform 1 to hot solution 3 of aluminum alloy 2 is illustrated. An process which forms aluminum composite material 4 (4 a through 4 f) with a layering structure comprising aluminum composite layer 12 and aluminum alloy layer 13 by the preform forming process and the aluminum impregnating process will be described in detail according to the following embodiments.

Embodiment 1

Referring to FIG. 1(a), alumina fiber 5 and powder of graphite 6 were mixed by stirring with stirring rod 31 in water in designated vessel 21. Alumina sol as an inorganic binder was added to water in which alumina fiber 5 and graphite 6 were being mixed. Alumina fiber 5 used had approximately 3 μm of average diameter, 50 cc/5 gf of an average length, chemical composition composed of approximately 95% of Al₂O₃ and approximately 5% of SiO₂, and graphite 6 used had approximately 20 μm of average diameter and chemical composition composed of 97% of C and approximately 3% of Al₂O₃ and SiO₂. Alumina sol 7 used was approximately 11% of Al₂O₃.

Aqueous solution 8 in which alumina fiber 5, powder of graphite 6 and alumina sol 7 being mixed was transferred to suction-forming device 22 from vessel 21. Suction-forming device 22 was connected to vacuum pump 23 and referring to FIG. 1(b), suctions water of aqueous solution 8 by vacuum pump 23 through filter 24. Accordingly, dehydrated-formed base material 9 in which graphite 6 were almost equally dispersed and coagulated to alumina fiber 5 was obtained. Then dehydrated-formed base material 9 was taken out from suction-forming device 22 and was sufficiently dried. (Not shown in Fig.)

Referring to FIG. 1(c), dehydrated-formed base material 9 was installed table 33 in the inside of heating oven 25 wherein the inside of heating oven 25 was under vacuum at 1×10⁻³ Torr by vacuum pump 23. The oven was heated up to approximately 1000° C. which was held for 2 hours while argon gas was being flown at the rate of 5 cc/min. And then desired preform 1 was obtained by cooling down to room temperature. (Not shown in Fig.) Further argon gas was continuously flown until the temperature was cooled down well while the oven was being cooled down. Over flown argon gas from the oven was exhausted from leak valve 32 to the outside. Thus the preform forming process can be carried out step by step.

Aluminum alloy 2 (JIS ACSA) was impregnated to preform 1 formed in the preform forming process above by pressurize casting. Hydraulic press machine 30 in FIG. 2 was used for pressurized casting. Extrusion portion 26 was installed at the lower portion of hydraulic press machine 30, and bush 28 in the inside of metal mold 27 installed on extrusion portion 26 was able to be taken out from metal mold 27 by moving extrusion portion 26 to upper direction after casting. Further, referring to FIG. 2 which is a partial cross section view of metal mold 27 and bush 28, the inventor describes the aluminum impregnating process. Referring to FIG. 2(a), bush 28 was installed in the inside of metal mold 27 and preform 1 preheated at approximately 550° C. was set to bush 28. A designated amount of hot solution 3 of aluminum alloy 2 at approximately 750° C. was injected to the upper portion of preform 1. Then as shown in FIG. 2(b) and FIG. 2(c), aluminum composite layer 12 a formed by impregnating hot solution 3 to preform 1 and aluminum alloy layer 13 composed of aluminum alloy 2 were integrally formed by pressing directly from upper direction with punch 29 of hydraulic press machine 30. Referring to FIG. 2(d), after removing pressure to lift up punch 29, layering structural aluminum composite material 4 composed of desired aluminum composite layer 12 in which aluminum alloy 2, alumina fiber and graphite 6 were mixed and aluminum alloy layer 13 was obtained by removing bush 28 from metal mold 27 by extrusion portion 26.

According to the manufacturing method above, three types of aluminum composite material 4 a, 4 b and 4 c which have different amount of graphite powder 6. Volumetric percentage (%) of graphite in each aluminum composite layer 12 of each composite material are 15% for aluminum composite payer 12 a of aluminum composite material 4 a, 11% for 12 b of 4 b and 7% for 12 c of 4 c, and volumetric percentage (%) of alumina fiber are 6.5% for 12 a, 12 b and 12 c. Further rest of the volume of aluminum layer 12 is attributed to aluminum alloy 2.

Embodiment 2

According to embodiment 2, a manufacturing method relates to sintering in hydrogen gas as a reducing gas in the preform forming process. After dehydrated-formed base material 9 which was formed according to embodiment 1 was well dried, it was put into heating oven 25 in which the inside was at 1×10⁻³ Torr under vacuum. Then nitrogen gas was introduced to substitute and after substitution, heating the inside of the oven was started. When the temperature reached to 400° C., approximately 100 cc/min of hydrogen gas was introduced and the inside temperature of the oven was held for 2 hours at approximately 1000° C. Hydrogen gas over flown from leak valve 32 was burnt using a pilot burner to prevent filling and explosion in the inside. Then the oven was cooled down to room temperature to form preform 1. Further during cooling down flow of hydrogen gas was stopped at approximately 400° C. and instead, nitrogen gas was flown. According to aluminum impregnating process as described in embodiment 1, hot solution 3 of aluminum alloy 2 was impregnated to preform 1 and aluminum composite material 4 d composed of aluminum composite layer 12 d and aluminum alloy layer 13 was obtained. Volumetric percentage (%) of graphite 6 was 15% of aluminum composite layer 12 d of aluminum composite material 4 d, volumetric percentage (%) of alumina fiber 5 was 6.5% and the rest was for aluminum alloy 2. According to embodiment 2, except hydrogen gas used in the inside of heat oven 25, the same materials, the same apparatus, the same method as described in embodiment 1 were used and the same signs representing each process were used and its explanation was omitted.

Embodiment 3

According to embodiment 3, a manufacturing method relates to sintering under vacuum in the preform forming process. Dehydrated-formed base material 9 which was formed according to embodiment 1 was put into heating oven 25 in which the inside was at 1×10⁻⁴ Torr under vacuum. Vacuum condition of the inside of the oven was held and the oven was heated up to approximately 1000° C., and the temperature of approximately 1000° C. was held for 2 hours and the oven was cooled down to room temperature to form preform 1. According to aluminum impregnating process as described in embodiment 1, hot solution 3 of aluminum alloy 2 was impregnated to preform 1 and aluminum composite material 4 e composed of aluminum composite layer 12 e and aluminum alloy layer 13 was obtained. Volumetric percentage (%) of graphite 6 was 15% of aluminum composite layer 12 d of aluminum composite material 4 d, volumetric percentage (%) of alumina fiber 5 was 6.5% and the rest was for aluminum alloy 2. According to embodiment 2, except vacuum condition of the inside of heat oven 25, the same materials, the same apparatus, the same method as described in embodiment 1 were used and the same signs representing each process were used and its explanation was omitted.

Embodiment 4

According to embodiment 4, a manufacturing method relates to form the preform by stirring and mixing alumina fiber 5 and activated charcoal 11 in water in vessel 21 in the preform forming process. Activated charcoal 11 having porous structure was used in which particle diameter was approximately 20 μm, chemical composition were 97% of C and approximately 3% of Al₂O₃ and SiO₂. Accordingly, except activated charcoal 11 used instead of graphite 6 used in embodiment 1, the same preform forming process and aluminum impregnating process as in embodiment 1 were carried out, signs representing each process were the same, and explanation was omitted. Volumetric percentage (%) of activated charcoal 11 was 15% of aluminum composite layer 12 f and volumetric percentage (%) of alumina fiber 5 was 6.5% and the rest was for aluminum alloy 2 in which of aluminum composite material 4 f comprised aluminum composite layer 12 f and aluminum alloy layer 13 formed as above.

Comparison Embodiment

According to comparison embodiment 1, a manufacturing method relates to sintering dehydrated-formed base material 9 in the air which was formed as well as embodiment 1 above in the preform forming process. Specifically, dehydrated-formed base material 9 which was formed by stirring and mixing alumina fiber 5 and graphite 6 in water in vessel 21, and dehydration and forming, was put into heating oven 25, and the temperature of approximately 1000° C. was held for 2 hours and the oven was cooled down to room temperature to form preform 10. According to aluminum impregnating process as described in embodiment 1, the aluminum alloy was impregnated to preform 10 and aluminum composite material 4 g composed of aluminum composite layer 12 g was obtained. Volumetric percentage (%) of alumina fiber 5 was 6.5% of aluminum composite layer 12 g of aluminum composite material 4 g, and the rest was for aluminum alloy 2. Specifically, only alumina short fiber 5 was remained in preform 10 because graphite 6 was oxidized and lost by heating in the air in the preform forming process. According to comparison embodiment 1, except the inside of oven 25 was in the air, the same materials, the same apparatus, the same method as described in embodiment 1 were used and the same signs representing each process were used and its explanation was omitted.

Comparison Embodiment 2

According to an implementation of comparison embodiment 2, a manufacturing method relates to sintering in the air in the preform forming process using activated charcoal 11 as well as described in embodiment 4. The same preform forming process and the same aluminum impregnating as embodiment 4 was carried out except that the inside of the oven 25 is in the air, and the signs representing were identical and an explanation was omitted. In aluminum composite layer 4 h composed of aluminum composite layer 12 h and aluminum alloy layer 13, aluminum composite layer 12 h comprised volumetric percentage 6.5% of alumina fiber 5 and the rest of alumina alloy 2 and no activated charcoal. As well as comparison embodiment 1, activated charcoal 11 was oxidized and lost by heating in the air during processing to form the preform.

An abrasion resistant property and a vibration damping property of each composite material formed according to implementation of each embodiment and comparison embodiment were tested by sliding property and damping property tests. Further hardness was measured by Vickers hardness test.

Sliding property test was carried out by surface pressure burdening designated cylinder-like chrome steel SCr420 (JIS G 4104) rotating at a circumferential velocity of 2 in/sec on the surface of each composite material aluminum layer 12 by 25 Mpa/min in automobile motor-oil 10W-30 to each test plate of each composite material. Surface pressure MPa when a burning-on took place was measured and tested burning-on property by the surface pressure value. The burning-on property was used as index of abrasion resistance property of each composite material.

In damping property test, vibration was provided by flipping the end with weight by hand in which an end of a test plate having a designated shape prepared from aluminum composite layer 12 of each composite material was grasped and a designated weight was installed to the other end. Frequency of vibration n when amplitude became % of the initial amplitude was obtained by amplitude and frequency of vibration detected by a strain-meter attached to the test plate, and then damping property Q was calculated from the below formula (1), and then vibration damping property of each composite material was relatively compared. Q=−(1/π)×(1/n)×1n(1/2)  (1)

Vickers hardness test was carried out following JIS Z 2244. Hardness was measured by pressing a designated quadrangular pyramid indenter on the surface of aluminum composite layer of each composite material with 98N.

The results of the sliding property test, the damping property test and Vickers hardness test are shown in FIG. 3. In addition to each embodiment and comparison embodiment of aluminum composite material, single aluminum alloy 2 was tested as comparison embodiment 3. Each aluminum composite material 4 a to 4 f formed according to embodiment 1 to 4 of the invention showed high performance in abrasion resistant property and vibration damping property in comparison with aluminum alloy 2. Especially, aluminum composite material 4 a to 4 e compounded with graphite 6 showed extremely high vibration damping property, which is representing excellent damping property based on graphite 6. Further, nevertheless softer graphite 6 or activated charcoal 11 than aluminum alloy 2 was compounded, Vickers hardness was almost equal to aluminum alloy and showed high hardness. Further aluminum composite material 4 a in embodiment 1 showed high abrasion resistant property and vibration damping property in comparison with aluminum composite material 4 g, which is representing the effect of sintering in argon gas of the invention.

When a structural photograph (FIG. 4) of aluminum composite layer 12 a of aluminum composite material 4 a and a structural photograph (FIG. 5) of aluminum composite layer 12 f of aluminum composite material 4 g were compared, graphite 6 was clearly confirmed in the former photograph, but it was difficult to confirm graphite 6 (void was confirmed) in the latter photograph. Specifically, as in the latter case, when it was in high temperature in the air to sinter dehydrated-formed base material 9, it was supposed that graphite was oxidized and lost. Further aluminum composite material 4 d implemented in embodiment 2, aluminum composite material 4 e implemented in embodiment 3 showed the same level of abrasion property and vibration damping property as aluminum composite material 4 a. Graphite 6 was prevented from being lost by sintering in argon gas, under vacuum and in a reducing gas, and the effect of compounding graphite 6 having high damping property and lubricative property was observed. Further, in case of compounding with activated charcoal as well as graphite 6, the abrasion resistant property and the vibration damping property of aluminum composite material 4 f implemented according to embodiment 4 and aluminum composite material 4 h implemented according to comparison embodiment 2 confirmed the effect of sintering in argon gas. Further, when activated charcoal 11 is compounded, loss of activated charcoal 11 can be prevented under vacuum and in reducing gas as well as compounding graphite 6 implemented in embodiment 2 and embodiment 3, and aluminum composite material having excellent abrasion resistant and vibration damping properties can be produced.

Further, when aluminum composite material 4 a, 4 b according to embodiment, and 4 c and aluminum composite material 4 f were compared, hardness and abrasion resistant property of aluminum composite material 4 f were in the same level as aluminum composite material 4 c. Specifically a composite material performing high abrasion resistant property and strong hardness can be produced by compounding activated charcoal. On the other hand, aluminum composite material 4 a to which graphite 6 was compounded has higher ability for vibration damping property than aluminum composite material 4 f to which activated charcoal was compounded. Specifically, a composite material having higher vibration damping property can be compounded with graphite 6 rather than activated charcoal 11.

Further thermal expansion coefficient of aluminum composite material 4 a according to embodiment 1 was 18.4×10⁻⁶/° C. (in the range of 20 to 150° C.) and thermal expansion coefficient of aluminum alloy 2 according to comparison embodiment 3 was 20.9×1 0⁻⁶/° C. Specifically aluminum composite material 4 a according to embodiment 1 can have an excellent effect that can lower the thermal expansion coefficient of aluminum alloy 2. A thermal expansion coefficient can be lowered by increasing the content of graphite 6 because the thermal expansion coefficient of aluminum composite material 4 c was 19.3×10⁻⁶/° C. Further, aluminum composite material 4 f to which activated charcoal 11 was compounded according to embodiment 4 can also lower the thermal expansion coefficient in comparison with aluminum alloy 2 as well as aluminum composite material 4 a. Accordingly, each aluminum composite material 4 according to embodiment 1 to embodiment 4 was thermally less deformed and excellently morphologically stable.

Further, it is an excellent advantage that aluminum composite material 4 a to 4 e can have the thermal conductivity equal to aluminum alloy 2 because graphite 6 has almost equal thermal conductivity to AC 8A of aluminum alloy 2.

In the manufacturing methods according to an implementation of embodiment 1 to embodiment 4, sintering temperature was approximately 1000° C., particle diameter of graphite 6 and activated charcoal 11 was approximately 20 μm, average diameter of alumina fiber 5 was approximately 3 μm and average length of alumina fiber 5 was 50 cc/5 gf. In other manufacturing method, sintering temperature can be in the range of approximately 600 to 1000° C., particle diameter of graphite 6 and activated charcoal 11 can be in the smaller range than approximately 100 μm, average diameter of alumina fiber 5 can be in the smaller range than approximately 10 μm and average length of alumina fiber 5 can be in the smaller range of 100 cc/5 gf. In such manufacturing method alumina fiber 5, graphite 6, and activated charcoal 11 can be adequately compounded to aluminum alloy 2. Accordingly aluminum composite material 4 which have high strength, excellent abrasion resistant and vibration damping properties can be produced.

In the manufacturing methods above according to an implementation of embodiment 1 to embodiment 4, the inside of oven 25 was in argon gas, under vacuum or in hydrogen gas to sinter in the preform forming process, but the inside oven 25 can be in helium gas or in nitrogen gas to be able to produce aluminum composite material 4 which has excellent abrasion resistant and vibration damping properties as well as above.

In the manufacturing methods above according to an implementation of embodiment 1 to embodiment 4, aluminum composite material 4 was obtained by integrally forming alumina fiber 5, graphite 6 or activated charcoal 11, aluminum alloy 2 and compounded aluminum composite layer 12, but also by setting amount of hot solution 3 of aluminum alloy 2 equal to impregnating amount to preform in aluminum impregnating process, aluminum composite material which has a structure in which alumina fiber 5, graphite 6 or activated charcoal 11 and aluminum alloy are being mixed can be produced. 

1. A method of manufacturing an aluminum composite material comprising the steps of: mixing alumina fibers, graphite, and an inorganic binder in water; dehydrating the mixture; forming a preform from the dehydrated mixture by sintering at a predetermined sintering temperature under vacuum, in an inert gas, or in a reducing gas; and processing to impregnate said preform with an aluminum alloy by pressure casting.
 2. A method of manufacturing an aluminum composite material comprising the steps of: mixing alumina fibers, activated charcoal, and an inorganic binder in water; dehydrating the mixture; processing to form a preform from the dehydrated mixture by sintering at a predetermined sintering temperature under vacuum, in an inert gas, or in a reducing gas; and processing to impregnate said perform with an aluminum alloy by pressure casting.
 3. A method of manufacturing an aluminum composite material according to claim 1; wherein particle diameters of said graphite are in the range of 0.1 μm to 100 μm.
 4. A method of manufacturing the aluminum composite material according to claim 2; wherein particle diameters of said activated charcoal are in a range of 0.1 μm to 100 μm.
 5. A method of manufacturing the aluminum composite material according to claim 2; wherein said activated charcoal comprises a porous structure.
 6. A method of manufacturing the aluminum composite material according to claim 1; wherein an average diameter of said alumina fiber is in a range of 1 μm to 10 μm, and; an average length of said alumina fiber is in a range of 10 cc/5 gf to 100 cc/5 gf.
 7. A method of manufacturing the aluminum composite material according to claim 1; wherein said sintering temperature is in a range of 600° C. to 1600° C.
 8. A method of manufacturing the aluminum composite material according to claim 1; wherein said aluminum impregnating process is adapted to form a layered structural material which comprises an aluminum alloy layer and a composite material layer in which the aluminum alloy is impregnated in the preform.
 9. A method of manufacturing an aluminum composite material comprising the steps of: mixing alumina fibers, graphite, and an inorganic binder in water; dehydrating the mixture; forming a preform from the dehydrated mixture by sintering at a predetermined sintering temperature under vacuum, in an inert gas, or in a reducing gas and under conditions to prevent a reaction between the graphite and the alumina fibers, while permitting the mixture to coagulate due to the presence of the inorganic binder; and processing to impregnate said preform with an aluminum alloy by pressure casting. 